# -*- coding: utf-8 -*-
"""
Created on Fri Sep 17 20:01:26 2021

@author: Think
"""

n=2
s=0
while n<=100:
    if(n%2==0): s=s+n
    else: s=s-n
    n=n+1
print('end,%d'%s)

"""
import math
print((-1)*((n-1)/2)+(n%2-1)*n)
利用2-3=-1，4-5=-1，只需判断最后一个数的奇偶
"""